1. Field of the Invention
This invention relates to a spindle for fitting vehicle wheel rims on workshop machines, particularly for tire-changing machines or the like.
2. The Prior Art
The use is known of so-called tire-changing machines that permit fitting or removing the tire onto and from the relevant rim of a wheel for vehicles, e.g., for carrying out maintenance jobs or replacing the rim and/or the tire itself. Such tire-changing machines generally consist of a base structure that supports a spindle for gripping and rotating a wheel rim, and of at least one tool arm having one or more tools suitable for removing and/or fitting the tire from and onto the rim.
Various types of spindle of known type exist.
A first type consists of a rim coupling plate, which is mounted on the base structure of the tire-changing machine so that it turns around a central work axis and which is provided with four rim gripping adapters.
The adapters are moving from the centre towards the outside of the plate, and vice versa, between a closing configuration, corresponding to the positioning of the adapters at the centre of the plate, and an opening configuration, corresponding to the positioning of the adapters at the periphery of the plate.
The adapter movement is by means of a rotating pinion arranged at the centre of the plate and which engages with four racks sliding longitudinally.
The outer ends of the racks are associated with the gripping adapters and push these to move when the rotor is driven in rotation by means of an independent gearmotor.
Once the rim has been secured on the coupling plate, this is caused to rotate around the central work axis.
These spindles of known type have a number of drawbacks including the fact that, in case of gearmotor malfunction or breakage of the racks or the pinion, the locking force of the gripping adapters can suddenly and abruptly go missing, with the risk of the wheel, rotating at high speed, coming off the coupling plate and jeopardizing the integrity of the equipment and the safety of the persons near the machine.
In a second type of spindle for tire-changing machines, the gripping adapters are caused to open and close by means of a pair of pneumatic cylinders. The cylinder rods, or the liners, are associated with the coupling plate while the corresponding liners, or the corresponding rods, are connected to two distinct gripping adapters; different spindles are however known in which the pneumatic cylinders are not connected to the coupling plate, but are interposed between two gripping adapters positioned opposite one another.
The pneumatic cylinders are arranged parallel to the direction of opening and closing of the two gripping adapters to which they are connected and directly control the opening and closing of the latter.
The remaining gripping adapters, on the other hand, are pushed moving by means of a particular kinematic lever system which is connected to the liners or to the rods, of the pneumatic cylinders and which transforms the movement of the cylinders themselves into the opening and closing movement of the adapters.
These spindles of known type also have a number of drawbacks.
In this respect the fact is underlined that the above lever kinematic system is usually rather complicated in terms of structure and the thrust force it can transmit to the gripping adapters to which it is connected is not constant during spindle opening and closing but, in fact, varies according to the position of the adapters.
Unfortunately therefore, the tightening of a wheel on the coupling plate can prove more or less successful depending on the size of the rim. It should also be taken into consideration that for this type of spindle as well, the previously made considerations are valid as regards the risks and the hazards which the personnel charged with operating the machine could encounter in case of breakdown; the malfunction of just one of the pneumatic cylinders in fact is enough to prevent the operativeness and correct operation of the machine. The main aim of the present invention is to provide a spindle for fitting vehicle wheel rims on workshop machines, particularly tire-changing machines or the like, that is practical, functional, and able to operate in conditions of utmost safety for the integrity of the equipment and the safety of the persons who find themselves near the machine.
A further object of the present invention is to be of simple construction, structurally sturdy and with a relatively low cost.